Idaho Code § 43-2535
The treasurer shall, at least one (1) month and not more than three (3) months before the expiration of the time of redemption of any property, serve or cause to be served, a written or printed, or partly written and partly printed, notice on the person or persons in the actual possession or occupancy of such land or lots, and shall also, within the same time, serve upon or mail to, the person in whose name the same stands upon the assessment records in the county assessor's office, a copy of said notice; which notice shall state when the delinquency certificate was made, in whose name the property was assessed, the description of the land or lots, the name of the local improvement district for which assessed, the amount of the assessment or installment, and when the time of redemption will expire. The treasurer shall, at the same time, send a similar notice, by mail, to each mortgagee or other holder of a recorded lien against such land, in each case where such mortgagee or lienholder has previously filed in the office of the treasurer a written request for such notice and paid the fee therefor, which request shall include the name and address of the mortgagee, the name of the reputed owner of the land, a description of the land and the date of the expiration of the mortgage or lien; no notice need be sent after the date of expiration, unless a further request therefor be duly filed. If the mortgagee or lienholder shall furnish a duplicate form of request for that purpose the treasurer shall certify thereon to the filing of the request and deliver the same to the party filing it. If there is no person in actual possession or occupancy of such land or lot and if the persons in whose name it stands, upon diligent inquiry cannot be found in the state, then the treasurer shall, within the same time, post or have posted, a copy of said notice in a conspicuous place upon said land or lots and in a substantial manner.
Whenever any notice is mailed, as herein required, the fact that the addressee does not receive it shall not in any manner invalidate or affect the proceedings herein provided.
Idaho Code § 43-2535